The deposition of metal layers on substrate surfaces is a well-known technique in the art to modify features of surfaces, like e.g. the optical appearance of the surface, the wear resistance, or the corrosion resistance of the surface. For the deposition of a metal layer on the substrate surface the surface is brought into contact with an adequate plating solution. In general, such plating solutions are aqueous electrolyte compositions comprising ions of the metal to be deposited as well as additional additives for the optimization of the plating reaction or the features of the metal layer deposited.
For the deposition of a metal layer on a substrate surface from an electrolyte comprising the metal to be deposited as an ion, a source of electrons is needed to induce the electrochemical reaction resulting in the metal deposition. Such source for electrons may be a reduction agent or an external current supplied to the substrate and a counter electrode. The deposition under utilization of a reduction agent is known as autocatalytic process or electroless plating. While electroless plating is used in various applications, especially for decorative issues, the metal deposition under use of an external current is often used for the deposition of metal layers having increased wear resistance or corrosion resistance of the surface.
In general, when it comes to the deposition of metal layers under use of an external electric current—in the following also referred to as electrolytic deposition—highly acidic or highly alkaline electrolyte compositions are used.
A principal problem associated with such electrolytic deposition is the occurrence of acidic or alkaline mist which is caused by the generation of gases, like e.g. hydrogen or oxygen, during the electrolytic deposition process. This mist is a healthy hazard and various ways of suppressing it have been attempted, incorporating mechanical and chemical approaches.
One chemical approach is to create a foam layer on the surface of the electrolyte used. This foam layer acts like a blanket to reduce airborne emissions of hazardous mist. However, a drawback of such foam layers is the accumulation of highly flammable gases, like e.g. hydrogen or oxygen, within the foam. To avoid explosions of the foam the equipment used for the plating process must comprise an explosion prove electrically installation. Furthermore, any kind of electrostatic charge which may cause some electrical sparks must be avoided. Both, the explosion proved electrically installation as well as the additional facilities to avoid electrostatic charge cause additional costs when setting up the plating system.
As a mechanical alternative to such foam layers, or in addition, exhaustions are used for the plating facilities. However, such exhaustion must be explosion proved, too.
UK Patent Application GB 2 250 515 A discloses a method for the electrolytic recovery of metal which comprises electrolyzing an acidic solution of the metal, the solution containing dissolved therein an ionic or cationic polyelectrolyte which is ionized under the electrolytic conditions employed and which possesses a hydrophobic moiety in the molecule such that the surface tension of the surface of the bath is reduced sufficiently to produce a foam.
US 2003/0111349 A1 discloses electrolytic solutions containing organic additives selected from a described class of additives (like e.g. 4,6-dihydroxypyrimidine) to reduce gas formation at the anodes of an electrolytic deposition process.
U.S. Pat. No. 5,468,353 discloses that the formation of acid mist or spray over metal electrowinning tanks, such as in the electrowinning of copper obtained by solvent extraction, is substantially inhibited or eliminated by electrowinning the metal from electrolytes containing certain fluoroaliphatic non-foam forming surfactants.
U.S. Pat. No. 4,484,990 discloses that the formation of acid mist or spray over metal electrowinning tanks, such as in the electrowinning of copper obtained by solvent extraction, is substantially inhibited or eliminated by electrowinning the metal from electrolytes containing certain cationic and/or amphoteric fluoroaliphatic surfactants.
US 2013/0056357 A1 discloses acid mist mitigation agents for electrolyte solutions. Sulfonates-, sulfate-, or carboxylate-caped, alcoxylated anti-misting agents are disclosed for use in a method of suppressing mist from electrolyte solutions.